Economics will always keep the crossings about the same price on each, i guess. well, as long as both still have empty capacity, and there's no scarcity power.
I think Eurotunnel is normally a bit more expensive, it's £24 because I'm travelling so early. For a weekend return it would be about £60. There again I haven't used a ferry since they wrecked my ZX12R during stormy weather a few years ago